Process engineering industrial installations are known in which temperature is a process variable to be recorded by metrology and supplied to an electronic controller for signal processing. Such process engineering industrial installations are used, for example, in petrochemistry, in energy and steam generation, in the food and luxury consumables industry and in general process engineering.
Known temperature sensors for such industrial installations include a fastening flange, by which a measuring resistor of the temperature sensor projects inside a container or a pipeline in order to record the temperature of the medium in the container or pipe here. Located outside the latter is the sensor head of the temperature sensor, which head accommodates electronic components, such as a measuring transducer for measurement signal conditioning, an optical display unit and the like, such that they are protected in a housing.
A temperature sensor is known from the brochure “Die neue Generation der Temperaturfühler für die Prozessindustrie” [The new generation of temperature sensors for the process industry] (ABB Automation Products GmbH, edition 04.2006, print number PB/TSP 100/300-DE). A high level of variance in uses which can be covered is achieved by a modular construction of standard components. The modular system essentially includes a sensor head with an integrated measurement insert, the electrical contact-connection of which on the part of the measuring resistor is achieved using contact-pressure springs. A measuring transducer may be optionally integrated in the sensor head and connected to the measurement insert. In order to protect these electrical and electronic components from external environmental influences, a sealed housing surrounds the sensor head. In order to protect the temperature sensor from the process conditions and to allow replacement without interrupting the ongoing process, a protective tube having process connections in the form of flanges or threads is provided, an outer neck tube in the continuation of the protective tube providing the connection between the protective tube and the sensor head. The sensor head can be used to effect the necessary connection of external cables to the measuring transducer which can be integrated therein and is intended to condition measurement signals.
Since aging of the components can be expected during operation of the temperature sensor, in particular in the case of high temperatures or temperatures which change frequently, industrial temperature sensors are designed with a replaceable measurement insert. However, so that the measuring transducer (also referred to as a transmitter) does not have to be exchanged as well at the same time as the measurement insert is changed, a cover which can usually be folded is mounted on the sensor head and is connected to the measurement insert using short connecting lines. The signal or bus line connections coming from a superordinate controller are placed directly on the measuring transducer. Therefore, although it is possible to replace the measurement insert without dismantling the measuring transducer after the connecting lines have been released on one side, this solution involves a hinged cover of a relatively considerable height, which can be disadvantageous, in particular in conditions of use with considerable vibration. However, this type of mounting is unsuitable for a screw cap if considered as an alternative to the hinged cover since the electrical connection lines would wind up when closing a screw cap.
Another known form of construction for temperature sensors which are intended for process engineering industrial installations provides for the measuring transducer to be permanently screwed to the resiliently mounted measurement insert. The above-described replacement of a measurement insert is no longer possible as a result of the permanent connection. In addition, should an optical display unit for displaying operating states and/or the current measured temperature also be concomitantly integrated in the sensor head, this is not possible in conjunction with the above-described mounting of the measuring transducer in a hinged cover since the measuring transducer occupies the only installation space in the hinged cover. In principle, although the display unit and the measuring transducer can form a common structural unit which can then be jointly mounted inside the sensor head, this can be unfavorable for the operability of a keyboard of the display unit.
It is known practice, in connection with screw-on covers, to directly mount the display unit on a measuring transformer which is connected to the measurement insert. With this form of construction, operation is possible after the cover has been unscrewed. However, the resilient mounting results in an undefined position of the display, which can be disadvantageous as regards the ability to read the display inside the housing which surrounds the sensor head and has viewing glass.
Another known form of construction provides for a display unit to be fastened in a stationary manner to a type of mounting bracket above the component combination of the measurement insert and measuring transformer. Although the display unit is thereby arranged in a stationary manner directly behind the viewing glass of a screw-on cover, a technically very complicated, electrically flexible connecting technique with respect to the measuring transducer is involved for implementation since the latter is fastened on the resiliently mounted measurement insert. This arrangement of the measurement insert with a measuring transducer mounted directly on it and with a display unit remote therefrom also results in a form of construction which is likewise very high, which is disadvantageous with respect to sensitivity to vibrations. In addition, exchange of the measurement insert is more laborious in comparison with the solutions discussed above since electrical connection lines of the display unit need to be separated from the measurements insert and the mounting bracket needs to be opened.